A pyroelectric type infrared sensor is one kind of an infrared sensor and comprises, as a detection pixel, a pyroelectric element in which a front face and a rear face of a pyroelectric substrate are respectively provided with electrodes.
A front face charge is present on the front face of the pyroelectric substrate by spontaneous polarization. In general, the front face charge attracts a floating charge of its surrounding so that the front face charge of the pyroelectric substrate is kept at an electrically neutral state if a temperature around the pyroelectric substrate remains constant.
A state of spontaneous polarization of the pyroelectric substrate changes according to a change in the temperature around the pyroelectric substrate. A change of a state of spontaneous polarization is more rapid than a response of a floating charge present around the pyroelectric substrate so that an electrically neutral state on the front face of the pyroelectric substrate is broken. As the result, the front face charge is generated on the front face of the pyroelectric substrate. The front face charge is taken out from an electrode as an output signal so that the pyroelectric element is used as a sensor. Most of pyroelectric type infrared sensors use the aforementioned pyroelectric element as their detection pixels and each comprises a group of sensor elements consisting of a plurality of pyroelectric elements.
As an example of a pyroelectric type infrared sensor, Patent document 1 discloses a pyroelectric type infrared sensor called compensation single type. The pyroelectric type infrared sensor comprises an electrode (photodetecting main element) which detects infrared radiation and an electrode (temperature compensation element) which monitors a temperature change of its surroundings to compensate the temperature change.
In Patent Document 1, a window portion of a shield case (outer can) of an infrared ray filter is provided with a filter. Infrared ray passes through the filter so as to be made incident on only the photodetecting main element. The temperature compensation element is shielded so as not to be affected from infrared ray incoming from outside.
Patent Document 2 discloses a dual type infrared sensor in which two pyroelectric elements having polarizing directions different from each other are connected in serial or in parallel.